1. Field of the Invention.
The present invention relates to housings for semiconductor devices and, more particularly, to housings for semiconductor devices having magnetic materials used therein which are to be protected from external magnetic fields.
Recently, the use of material layers which have high magnetic permeability in monolithic integrated circuits has provided a basis for magnetic field sensors and for magnetic cell memories. Typically, such a magnetically permeable layer is formed of a thin film of a metallic alloy composition which, as an example, might comprise nickle, cobalt and iron.
Such permeable thin films are fabricated in the course of the fabrication procedure for monolithic integrated circuits with some added steps, and are often provided by vacuum deposition methods, though other metheds can be used. The films so fabricated usually exhibit uniaxial anisotropy, magnetoresistance, and are usually chosen with such a composition of the foregoing elements that there is little magnetostriction.
Because very large demagnetizing fields would otherwise result, the magnetization of such thin films will always lie substantially in the plane of the film, that is, the magnetization vector for the material will be substantially in the plane of the film. The orientation of the easy axis of magnetization can be chosen if the film is deposited in the presence of a magnetic field oriented in the selected direction.
In integrated circuit devices having such permeable thin films, the orientation of the magnetization vector in the plane is usually important to the operation of the device. In accord with thermodynamics, the magnetization in such a film will arrange itself to minimize the magnetic energy. Fields external to the film will often be generated in and about the device as part of the device operation. These fields must be oriented to have components in the plane of the magnetic thin films to have a significant effect on the magnetization of such films in accord with minimizing the magnetic energy. Fields perpendicular to the films will have no effect on such magnetization.
On the other hand, for those magnetic fields which are generated from sources external to the film and to the integrated circuit device and its housing, there will be a desire in many instances that part or all of them have no significant effect on these permeable films. This is particularly true in the case of memory devices where the information contained in the memory is contained in the orientations of the magnetization vectors of the magnetic material used in each memory cell. Any such external magnetic field effects which would alter the orientations of the magnetization vectors in the memory cells could contribute to a loss of information or to erroneous information being provided by the memory.
Thus, such films need to be protected from external magnetic field disturbances but the integrated circuit structures must also be housed in such a way to minimize cost if they are to remain a viable product for the memory market. Therefore, a housing to protect such integrated circuit structures from significant external adverse influences, including external magnetic fields, and which can be economically provided, would be desirable.